Strict standards were set for light distribution in the field of traffic technology which can be achieved by providing lens arrangements arranged in front of the illuminants. Signal optics with lens arrangements have therefore been known for a long time, see e.g. DE 42 25 139 A1, in which a converging lens and a dispersing lens are arranged in front of an illuminant to achieve the desired light distribution.
In the meantime light diodes have become accepted as illuminants in variable message signs, which, as is known, have a long life and provide a high intensity of light. An essential aspect is the phantom light, i.e. sunlight impinging onto the LED, which is reflected by the LED and which may lead to deceptions to the road users when the position of the sun is unfavorable. For this, legal regulations exist that must be obeyed in the sense of traffic safety.
EP 0 930 600 A1 is an example for an optical element in variable message signs, in which the problem of phantom light is explicitly discussed. In this device, the light irradiated by an LED is bundled by a converging lens and is conducted to a dispersing lens arranged at a distance to the converging lens. By a suitable design of the converging lens, the light may be distributed according to the demands. The disadvantage is the large distance between the converging lens and the dispersing lens that is necessary to avoid phantom light as well as the factual necessity to arrange a screen in the area of the focal spot of the converging lens so that the relevant regulations for light distribution and phantom light are fulfilled.
In order to further increase brightness of the light emitting diodes, the LEDs are permanently improved, e.g. by an improved reflection of the light which is actually emitted backwards. This was most of all achieved by the use of modern reflectors within the LEDs so that extremely powerful LEDs are available nowadays. When using modern LEDs the potentially higher phantom light must be prevented by suitable measures.